This invention relates to an electronic musical instrument, more particularly a device for generating note codes by utilizing equally spaced binary codes.
In a digital electronic musical instrument, for the purpose of producing a musical tone having a frequency corresponding to the tone pitch of a depressed key of a keyboard, a binary code is used to produce a key code signal representing the depressed key.
In the case of an electronic musical instrument having 61 keys, for example, key informations or codes identifying respective ones of the 61 keys (5 octaves plus one key) are generally expressed by standard binary codes as shown in Table I, and 12 tone names are assigned as shown in the following Table II based on this concept.
TABLE I ______________________________________ Data number to be designated Binary code ______________________________________ 1 0000 2 0001 3 0010 4 0011 5 0100 6 0101 7 0110 8 0111 9 1000 10 1001 11 1010 12 1011 13 1100 14 1101 15 1110 16 1111 ______________________________________
TABLE II ______________________________________ Key code Note Binary code of Binary code of Octave name octave data note name data ______________________________________ 1 001 2 010 3 011 4 100 5 101 6 110 C .0000 C.music-sharp. .0001 D .0010 D.music-sharp. .0011 E .0100 F .0101 F.music-sharp. .0110 G .0111 G.music-sharp. .1000 A .1001 A.music-sharp. .1011 B .1011 ______________________________________
In the case of Table II, the note name data representing 12 note names C, C.sup..music-sharp. . . . B assigned to fractional parts (i.e. below radix point) of the key codes and the octave data representing the octaves are assigned to integer portions of the key codes. In order to discriminate 12 tone names four bits are required and to discriminate 6 octaves 3 bits are required.
When respective note names C, C.sup..music-sharp. . . . B are respectively assigned to the first to 12th binary codes ".0000"-".1011" as shown in Table II, the key codes of the chromatic notes in the same octave are expressed by an equal interdigit spacing that is ".0001" and the first to sixth octaves repeat cyclically the binary codes of ".0001"-".1000". However, the interdigit spacing corresponding to one semitone step at a transition of from one octave to the other becomes ".0101". In other words, the spacing between the binary code of the note name B and the binary code of the note name C of the next octave is ".0101", and thus all spacings are not equal.
One method of producing a musical tone from an electronic musical instrument is a method of reading out a waveform memory device. According to this method, sampled amplitude values of a waveform to be produced are prestored in a waveform memory device and the stored values are sequentially and repeatedly read out by an address signal having a frequency determined by the key code thereby forming a musical tone waveform.
To form a read out address signal it has been proposed to regularly and repeatedly accumulate a frequency number signal having a magnitude corresponding to a numeral (hereinafter called frequency number) proportional to the frequency of a tone to be produced so as to form a saw tooth shaped repetitively progressive signal having a frequency corresponding to the magnitude of the frequency number from the accumulated value. Then the repetitive frequency signal is read out and used as the address signal.
Thus, the reading and addressing operation of the waveform memory device is performed in each period of the address signal thereby producing a musical tone signal having a frequency corresponding to the frequency number.
When producing a musical tone according to this method, it is essential to obtain a frequency number signal proportional to the tone pitch, i.e., frequency of each key of the keyboard. In this manner, it is possible to cause respective generated tones to have predetermined pitches corresponding to respective keys. According to the prior art method, however, since the key code signals have been assigned to 12 note names by using standard binary codes having 16 values, when transferring from one octave to the other, the content (value) of the key code can not maintain an equal difference. For the purpose of giving a linear proportional relationship to a portion not having the equal difference, the prior art electronic musical instrument has been constructed as follows:
More particularly, as shown in FIG. 1, there is provided a frequency number signal generator 1 having a ROM capable of storing linear numerical information over the entire tone range of the keyboard. A key code signal KC, containing key codes shown in Table II and formed by a key assignor 4 acting as a depressed key detector and operated by a key switch 3 responsive to a depressed key 2, is applied to the ROM in the frequency number signal generator 1 to act as an address signal.
Then, a numerical value output having a magnitude corresponding to a key designated by the key code signal KC is read out from the ROM in the frequency number signal generator 1 and the output is sent out as a frequency number signal F which has a content regarding the numerical value information (i.e. the frequency numbers) having a linear characteristic over the entire tone range of the keyboard.
The frequency number signal F is multiplied with the output PT of a pitch modifying data generator 5 in a multiplier 6 for applying an effect to the musical tone. The product F.multidot.PT is applied to a accumulator 7 as an input to be accumulated. The accumulator 7 sends its accumulated value to a musical tone wave generator 8 including a waveform memory device to act as a read out address signal. This prior art electronic musical instrument is disclosed in U.S. Pat. No. 3,979,996 dated Sep. 14, 1976 and invented by Tomisawa et al.
In the prior art electronic musical instrument shown in FIG. 1 it is essential to convert a key code signal KC not having a linear equal difference relationship at a portion of the numerical value content into a numerical data information having a linear equal ratio relationship in the frequency number signal generator 1.
While in the circuit shown in FIG. 1, a pitch modifying effect is applied by the multiplier 6, its construction is extremely complicated for effecting addition of a plurality of partial integrations. To simplify the multiplier 6, the frequency number signal generator 1 shown in FIG. 1 has been modified such that it does not directly memorize the linear frequency number F but, rather, memorizes the same after converting it into a logarithmic value log F and applies the logarithmic value log PT of the linear numerical information value PT to the pitch modifying data generator 5. Log PT and log F are added together by an adder sustituted for the multiplier 6 shown in FIG. 1, and its output log F+log PT=log F.multidot.PT is converted by a lagarithm-linear converter, not shown, into a linear numerical value information F.multidot.PT which is applied to the accumulator 7 as an input to the accumulator. This modified electronic musical instrument is disclosed in Chibana et al U.S. Pat. No. 4,215,614 issued Aug. 5, 1980 entitled "Electronic Musical Instruments of Harmonic Wave Synthsizing Type".
As above described, in the prior art waveform memory device read out type digital electronic musical istrument, in order to obtain a frequency number signal F in the form of linear numerical information it is necessary to use a ROM adapted to directly store a plurality of frequency numbers F corresponding to respective tone pitches over the entire tone range of a keyboard after converting the frequency numbers F into logarithmic values. In addition, in order to apply an effect, it is necessary to provide a multiplier of a complicated construction or an adder and a linear-logarithm converting circuit. For this reason, simplification of the entire construction has been limited.